University of Wisconsin
Measuring Stresses in Metal Plate Connectors
Mechanical Engineering researchers (Brian Bauman and Prof. Bob Rowlands) at the University of Wisconsin-Madison, in conjunction with the USDA Forest Products Laboratory (Ron Wolfe), are using Thermoelastic Stress Analysis to measure the stresses in metal plate connectors such as those commonly found in wood frame trusses. The following figures show a 3x5 in. commercial connector plate butt-joining two standard 2x4's. The joint was incrementally loaded longitudinally at 2 Hz to failure and the stresses were recorded with a Stress Photonics' DeltaTherm 1000. Total scan time per image was approximately 5 minutes. Figure 1 shows the plate connector cycled between 500 and 2500 lb, whereas Fig. 2 shows the same metal connector near failure when loaded from 1000 to 4000 lb tension. Most truss failures occur at a joint. Objectives of this study are to develop improved design methods and to optimize such connections, thereby saving both metal and wood.
